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之前有过区域赛，简化版问题： 给定一个小写字符组成的字符串S，（|S|<1e5，下标从1开始）,现在有Q种操作，对于每个操作Q(Q<=1e5)，输入opt， 如果opt==1，输入x，c，表示把S[x]改为c，（c是小写字母）。 如果opt==2，输入L，R，和字符串T，输出S[L-R]中有多少个字 阅读全文
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Mr. Fib is a mathematics teacher of a primary school. In the next lesson, he is planning to teach children how to add numbers up. Before the class, he 阅读全文
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Median Sum You are given N integers A1, A2, ..., AN. Consider the sums of all non-empty subsequences of A. There are 2N−1 such sums, an odd number. Le 阅读全文
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Each of Farmer John's N cows (1 ≤ N ≤ 1,000) produces milk at a different positive rate, and FJ would like to order his cows according to these rates 阅读全文
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题意：求有向图里面有多少个三元环。 思路：枚举起点A，遍历A可以到的B，然后求C的数量，C的数量位B可以到是地方X集合，和可以到A的地方Y集合的交集（X&Y）。 B点可以枚举，也可以遍历。（两种都试过，区别不大。） 枚举代码： 遍历代码： 阅读全文
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You are given N sets, the i-th set (represent by S(i)) have C(i) element (Here "set" isn't entirely the same as the "set" defined in mathematics, and 阅读全文